With the maturity of automatic document technologies, automatic document feeders are widely used in a diversity of document processing machines such as printers, copiers and multifunction peripherals. The automatic document feeders are used for successively feeding a stack of documents into the inner portion of the document processing machine so as to implement associated operations and achieve the labor-saving purpose.
The conventional automatic document feeders, however, still have some drawbacks. For example, the conventional automatic document feeder is only designed to feed the documents into the inner portion of the document processing machine. In other words, the manufacturer of the conventional automatic document feeder does not consider whether the spacing between any two successive documents in the feeding path is equal. In a case that the conventional automatic document feeder is applied to a sheet laminating apparatus, the automatic document feeder becomes hindrance from operating the sheet laminating apparatus.
FIG. 1 is a schematic view illustrating the application of a conventional automatic document feeder to a sheet laminating apparatus. The conventional automatic document feeder 11 comprises a sheet pick-up roller 111 and a sheet feeding channel 112. The sheet feeding channel 112 is arranged between the sheet pick-up roller 111 and a sheet laminating mechanism 12. A sheet ejecting path 13 is arranged at the outlet of the sheet laminating mechanism 12. The sheet pick-up roller 111 is used for successively feeding multiple documents 14 into the sheet feeding channel 112. When the documents 14 are fed into the sheet laminating mechanism 12 through the sheet feeding channel 112, the documents 14 are subject to a heating and pressing operation (also referred as a laminating operation) by the sheet laminating mechanism 12. After the heating and pressing operation is performed, the documents 14 are covered with a protective film 15, thereby ejecting corresponding film-covering documents 16 to the sheet ejecting path 13. Next, the film-covering documents 16 are transported across an automatic cutting mechanism 17. The cutting lines 19 of these film-covering documents 16 are successively cut by the automatic cutting mechanism 17, so that the film-covering documents 16 are cut into multiple separate laminated documents 18. Ideally, the spacing interval between any two film-covering documents 16 should be identical. If the spacing intervals between the adjacent film-covering documents 16 are not identical, the positions of some cutting lines 19 are improper. Under this circumstance, the sizes of the laminated documents 18 are different or the laminated documents 18 are possibly damaged.
For solving the above drawbacks, the spacing interval between any two adjacent documents in the sheet feeding channel should be kept constant.
In accordance with a conventional method for controlling a constant spacing interval between any two adjacent documents, the documents are successively fed into the sheet feeding channel by the sheet pick-up roller at a constant time interval or at a specified distance between any two documents. Since the documents are transported by the sheet pick-up roller due to a friction force, the time periods required for feeding the documents into the sheet feeding channel are usually different. In other words, the conventional method fails to achieve the purpose of controlling a constant spacing interval between any two adjacent documents.